Automatic shut off valves have been used to shut off the gas supply to a structure during an earthquake. The shutoff of the flow of gas from pipes that may be ruptured during an earthquake prevents a fire or explosion due to a gas leak caused by the earthquake.
The automatic shut off valves are typically installed in a gas flow line. The existing automatic shut off valves use mechanical mechanisms to sense the shock and vibrations of an earthquake. Some of the automatic shut off valves use a metal ball which is displaced by the force of an earthquake from its normal rest position to cause the valve to close.
Other automatic shut off valves use a pivoted flapper arm that is held in open position (i.e., out of the line of the gas flow) by a holding magnet embedded in it. When the magnetic attractive force is reduced (e.g., an electromagnet may be activated after an earthquake, which opposes the field of the holding magnet), the pivoted flapper arm swings down by gravity into the closed position and a flapper seal element seals the valve seat. The flapper arm may also be released by a ball that normally rests in a cavity above the flapper's magnet to keep the flapper up and the valve open. The ball moves away from its resting position by the force of an earthquake causing the flapper to be released to close the valve.